Several methods are earlier known for treatment of difficult wounds, such as infected wounds, diabetes wound, pressure sore or deep wounds.
Drainage of for instance operation wounds or other liquid discharging wounds with the aid of negative pressure is a standard treatment that has been used for decades. An example of a manual suction pump for said use is described in U.S. Pat. No. 3,742,952.
In said publication is described a pump in form of an elastically compressible body of an open-cell foam, preferably a polyurethane foam. Said body also serves as a canister for exudate drained from the wound. It is stated that the pump has a capacity to hold a negative pressure of 15-80 mmHg more than 48 hours. A drainage tube is arranged with a perforated end part in the wound cavity and via tube connected to the pump.
A similar device is described in U.S. Pat. No. 4,525,166. In the description of said publication is specifically stated that the negative pressure in addition to drain wound fluids from the wound also presses the edges of the wound together, thereby stimulating rapid tissue granulation and healing of the wound. The two mentioned publication thus teach that vacuum treatment of wounds stimulates the healing of the wounds.
The terms vacuum treatment, treatment at a reduced pressure and treatment with negative pressure are alternatively used in the literature. When using any of this terms in the present description the terms always concern treatment at pressure below normal atmospheric pressure.
Treatment of deep wounds have earlier also been performed by adding an irrigation liquid to the wound and then draining the injected liquid and pus and bacteria present in the wound before the irrigation. Examples of such devices are described in U.S. Pat. Nos. 5,385,494 and 4,382,441.
Extensive investigations of the effect of continuous and intermittent treatment of wounds under negative pressure, i.e. pressure below atmospheric pressure, were performed in the 1980's at Russian institutes. One was able to establish that difficult and normally slow-healing wounds healed considerably faster with the aid of vacuum treatment compared with conventional treatment.
One was inter alia also able to show that treatment at a reduced pressure provides a significant antibacterial effect. Said Russian investigations are described in several articles in the Russian medical journal Vestnik Khirurgii. The relevant articles from said journal are:                1) Kostiuchenok et al, September 1986, pages 18-21.        2) Davydov et al, September 1986, pages 66-70.        3) Usupov et al, April 1987, pages 42-45.        4) Davydov et al, October 1988, pages 48-52.        5) Davydov et al, February 1991, pages 132-135.        
In an article by Chariker et al in the journal Contemporary Surgery, No. 34, June 1989 is stated that vacuum treatment stimulate tissue granulation and contraction of wounds, which with conventional treatment are very difficult to heal.
Vacuum treatment of wounds is also described in U.S. Pat. Nos. 4,969,880, 5,645,081, 5,636,643, 6,855,135 B2 and WO 2006/025848 A2.
Hitherto known devices for vacuum treatment of wounds are not satisfactory in every respect. For instance U.S. Pat. No. 5,645,081 describes a wound pad in form of an open-cell foam. It is believed that cell growth are stimulated when tissue can grow into the pores of the foam but there is also a risk that the formed tissue fasten in the pores and is damaged when the pad is removed from the wound. There is a demand to improve wound pads for use in severe and deep wounds.